Police are investigating the tragic death of Christina Grimmie, who was shot dead at age 22 in Florida.

The singer, The Voice alum and YouTube star and the pop rock group Before You Exit, who she had opened for, were signing autographs for fans inside Orlando's Plaza Live Theater after their concert ended when a man opened fire and shot her. She later died of her wounds.

Christina is survived by her parents, Tina and Albert Grimmie, and brother Marcus Grimmie, who was hailed as "hero" for attempting to apprehend the shooter. Christina's manager, stepfather of Selena Gomez, who she had toured with in the past, has set up a GoFundMe page to help the family.

The shooter fired multiple times and was the sole assailant: The gunman approached Christina alone, wielding two handguns, as well as two loaded magazines and a large hunting knife before firing at the singer, police said. About 120 people were in The Plaza Live at the time of the shooting.

Christina was later hospitalized and died from the gunshot wounds she suffered, police said.

A witness, Josh Call, told The Orlando Sentinel he was outside the venue working a vegan hot dog stand and heard four or five gunshots.

"It was quick like pow, pow, pow, pow," he said.

He said a security guard rushed to make sure others were out of harm's way and that after a few minutes, he went inside and saw a woman on the ground, bleeding from the head as someone gave her chest compressions.

A Twitter user who said she witnessed the shooting tweeted she "was standing five feet away" the shooter and ran after he opened fire.

"He was behind me," she wrote. "I looked this guy in the eyes and smiled at him completely unaware of his intentions. It's a sick world we live in."

Another Twitter user who attended the concert posted a video of Grimmie performing onstage at the venue. She said Before You Exit member Riley McDonough told fans to "run, get in your cars and go home—there were gunshots."

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What kind of security was at the venue? An Orlando Police Department spokesperson told E! News there were no metal detectors at the venue. Police also said there was private security there at the time of the shooting, but they were not armed law enforcement officers. There were also no OPD officers hired by the venue to work extra duty Friday night.

Also, fans' purses and backpacks are typically checked when they enter the venue, Mina said, according to NBC News.

A message posted on the Plaza Live Theater's Facebook page said the venue was working with police in their investigation and that all activities and events have been suspended until further notice.

"Like everyone else in the community, the board and staff at the Plaza Live Venue are deeply saddened by the tragic events of Friday evening," the post read. "Our thoughts and prayers are with the families of those lost as well as those who witnessed and aided in the recovery after this senseless act."

The shooter targeted Christina? "The suspect traveled to Orlando apparently to commit this crime and then had plans to travel back to where he came from," Mina told reporters Saturday, according to NBC News.

The shooter's motive remains unknown: The outlet reported detectives were scouring the man's cellphone and computer to find a motive for the killing and that Mina said there was "no indication" so far that he knew Grimmie.

Autopsy is complete: E! News has confirmed that an autopsy was performed on Christina Saturday morning and that cause of her death was ruled a homicide. The investigation continues.